1. Field of the Invention
The present invention relates to methods for manufacturing a semiconductor device.
2. Description of the Related Art
In the process of manufacturing a semiconductor device, a method of forming contact plugs separately in two or more steps can be used to prevent contamination by metal in a circuit portion and reduce manufacturing variation in the contact plugs, or for other purposes, at the time of forming openings of the contact plugs. For example, Japanese Patent Laid-Open No. 2011-29604 and No. 2008-227357 disclose a method including two contact plug formation processes. Here, each contact plug formation process is accompanied by, for example, an etching process and a metal removal process, and as more contact plug formation processes are performed, (inter-layer) insulating layers become thinner, resulting in a possible electrical short circuit or reduced stress resistance of the semiconductor device.
It is also conceivable to provide in advance an insulating layer having a thicker film thickness in the semiconductor device. However, it is not desirable from a manufacturing viewpoint to form an opening of a contact plug on such an insulating layer with a thick film thickness, which leads to change in an aspect ratio (a ratio between the depth and width of the opening).